1. Technical Field
The present invention relates to a vehicle behavior control apparatus that controls a steering angle.
2. Related Art
Known techniques acquire a curvature radius of a curve, along which a vehicle is turning, and control a steering angle of the vehicle by using the acquired curvature radius.
For example, Japanese Patent No. 4596063 discloses a technique such that the curvature radius of the curve on the road is calculated on the basis of first to third distances from the own vehicle to a road boundary or a road accessory in front of the own vehicle detected by a vehicle-mounted radar device. The first distance is a distance from the middle position of the front end of the own vehicle along the vehicle width direction to the road boundary or the road accessory. The second distance is a distance from the right edge of the front end of the own vehicle to the road boundary or the road accessory. The third distance is a distance from the left edge of the front end of the own vehicle to the road boundary or the road accessory. Further, in the disclosed technique, an optimal distance from the middle position of the front end of the own vehicle to the road boundary or the road accessory is calculated on the basis of the curvature radius of the curve. A steering angle of the own vehicle is controlled so that an actual distance from the middle position of the front end of the own vehicle to the road boundary or the road accessory is adapted to the calculated optimal distance. In the disclosed technique, the optimal distance is a distance from the middle position of the front end of the own vehicle to the road boundary or the road accessory when the own vehicle is traveling along a circular trajectory of the proper curvature radius in the curve on the road.
The technique disclosed in Japanese Patent No. 4596063, however, fails to automatically control the steering angle while smoothly changing the steering angle. This is true for the case of traveling along an alternate sequence of right- and left-hand curves (e.g., a right-hand curve->a left-hand curve->a right-hand curve-> . . . ) without a straight path therebetween.
In such a scenario, there is an inflection area on the road between each right- or left-hand curve and its subsequent left- or right-hand curve, where, for example, the boundary of the road situated in front of the own vehicle may change abruptly from an outer boundary of the right- or left-hand curve to an outer boundary of the left- or right-hand curve. Consequently, in each inflection area, an actual distance from the front end of the own vehicle to the road boundary in front of the own vehicle (referred to as an actual road boundary distance) may increase abruptly.
Since the optimal distance defined in Japanese Patent No. 4596063 is a distance from the front end of the own vehicle to the road boundary in front of the own vehicle when the own vehicle is traveling along a circular trajectory of the proper curvature radius of the curve, an optimal distance may not change abruptly in each inflection region while the own vehicle is traveling along the right- or light-hand curve.
The technique disclosed in Japanese Patent No. 4596063 is configured to control the steering angle so that the actual road boundary distance is adapted to the optimal distance. In each inflection region, however, since the actual road boundary distance may change abruptly without an abrupt change in optimal distance as described above, the steering angle may be controlled to change abruptly.
In consideration of the foregoing, it would therefore be desirable to have a vehicle behavior control apparatus capable of controlling a steering angle while smoothly changing the steering angle.